Electrical fuse



Oct. 31, 1944.

S. l. LINDELL ELECTRICAL FUSE Filed March 23, 1936 7 Sheets-Sheet l Oct.31, 1944. s. 1. LlNDELL P ELECTRICAL FUSE Filed March 25, 1936 7Sheets-Sheet 2 Oct. 31, 1944. s. 1. LINDELL 2,361,638

ELECTRICAL FUSE Filed March 25, 1936 TSheets-Sheet 3 .7 $20322 for 52'ardfizffldell.

Oct. 31, 1944. s U L 2,361,638

ELECTRI CAL FUSE Filed March 23, 1936 7 Sheets-Sheet 4 In z/enfian'i'gurdf Z92 dZZ Oct. 31, 1944. s. 1. LINDELL 2,361,638

ELECTRICAL FUSE I Filed March 23, 1936 7 Sheets-Sheet 5 K 19 0/ @J9 J f4 49 0 1 00 6 U2 w a 0 1 9 1 t /55 $1 [I w:-

Oct. 31, 1944. s. 1. LINDELL ELECTRICAL FUSE Filed March 23, 1936 7Sheets-Sheet 6 Patented Oct. 31, 1944 ELECTRICAL FUSE Sigurd I. Lindell,Chicago, 111., assignor to Schweitzer & Conrad, Inc., Chicago, 11]., acorporation of Delaware Application March 23, 1936, Serial No. 70,280 I.69 Claims.

My invention relates generally to electrical circuit opening devices andit has particular relation to fuses.

While the present invention is particularly applicable to fuses of lowcapacity, i. e. of the order of ten amperes or less, the invention isnot to be limited to such low capacity fuses, sincethe teachings of thepresent invention have application to capacities of any desired value.The invention disclosed herein relates to certain of the subject matterdisclosed in the copending application of Hugh A. Triplett, Serial No.758,372, filed December 20, 1934, and assigned to the assignee of thisapp Fuses are commonly used in preference to the more expensive relaycontrolled circuit breakers for the purpose of isolating branches ofhigh tension feeder circuits in the event of heavy overloads or shortcircuits, especially in sparsely populated districts where light loadsare supplied and the revenue is small. Ordinarily, the load current isvery low in such installations and the current required to beinterrupted b a fuse on short circuit is rather limited, because of thehigh impedance between the point of fault and the generating source.This is particularly true where fuses are applied on the primaryside ofa small distribution transformer, the impedance of which is usuallysuiiicient to limit the primary current to a few amperes in the event ofsecondary short circuit,

It is obvious that the fuses used under such conditions must be capableof being blown by low currents and that their time-current blowingcharacteristicsmu'st be dependable and permit of rather accuratecoordination with the available blowing currents in such particularinstallations. Also, it is required that the fuses be capable ofinterrupting low currents Without prolonged arcing in order not toimpair the protected equipment or the further use of the fusereceptacle.

Air break fuses of the expulsion type are frequently employed in suchinstallations. A typical embodiment comprises a fibrous insulating tubewith a metal ferrule at each end constituting terminals for a' renewablefuse link. Usually, one end of the tube assembly is closed and thefusible section of the link is positioned at this end. The fusing of thelink by overcurrent is intended to suddenly create a sufficient volume fv por and as o xpel one of the terminals of the fuse link from theinsulating tube, thus lengthening the arc and interrupting the currentflow, with a minimum of arc duration and attendant erosion ordestruction of the tube or fuse link receptacle.

Experience has shown, however, that the plain expulsion fuse, asordinarily dimensioned and constructed, and to be found in great numberson distribution systems, although it is capable of generating sufficientgas pressure to expel one terminal and interrupt a heavy overloadpromptly, frequently fails to cope with currents of limited magnitude.For this reason, mechanical means have been incorporated in more recentdesigns to initiate the lengthening of the are upon the blowing of thefusible section. These means impose mechanical tension upon the fusiblesection and the amount of this tension varies appreciably in variousmakes of cutouts and may run from 1 or 2 lbs. to 10 lbs.

In certain fuses of this general type, the fusible link has comprised aplain current calibrated fusible section which is placed directly intension as by a spring, weight or the like. In such combination, thefusible section does not actually fuse upon the occurrence of relativelylight blow ing currents, but ruptures before the meltin point has beenreached, and the time-current characteristic depends not only upon thelink but also upon the tensio imposed upon it by the particular fuseassembly. in which the link is applied, and may vary greatly.

Another embodiment is found in the patent to Conrad, No. 1,446,423. Inhis device, a high resistance strain wire has been applied in parallelwith the fusible section proper, to relieve the latter of the mechanicaltension imposed on the link assembly by the actuating spring. Thisrenders the time-current characteristic practically independent ofwhatever tension may be imposed on the link, in the case of fuse linksof comparatively high current rating where the current carrying capacityof the strain wire can be made negligible as compared with the fusiblesection proper.

Now it is apparent that a fuse link, in order to be universallyapplicable in various makes of fuse receptacles or cutouts, must possessa minimum tensile strength to providea margin above the highestmechanical tension imposed by any cutout in common use, and to withstandthe tension that may be imposed by a lineman during the process, ofre-fusing a cutout. I have found that in'low current links of ratings upto 10 amperes, any strain member, capable of meetin this condition,possesses sufficient current carrying capacity in itself to make itimpossible to use a parallel fusible section for the purpose ofrendering the time-current characteristic independent of the mechanicaltension that might be imposed. I

I find that for fuses of small current carrying capacity, that is, ofthe order of 10 amperes or less, and for voltages of the order employedon the primary sides of distribution transformers, a high tensilestrength wire is preferably employed for the fusible element. A suitablewire for this purpose is Chromel A or Nichrome V, both consisting of anickel chromium alloy of high melting point.

When such a high tensile strength wire is employed as the fuse link, arelatively high temperature is required to cause it to part. Thus, undernormal operating conditions, and particularly under overload conditions,the temperature of the fuse wire may be raised to a relatively highvalue. As a result, due to the heat thrown off by the fuse wire, thefiber tube enclosing the fusible section and even the fibrous lining ofthe tubular receptacle in which the link is placed, may be severelycharred. In some instances the tube or sleeve surrounding the fuse linkhas been so severely charred that it has been necessary to renew notonly the fuse link but also the sleeve or tube housing it. To overcomethe disadvantages of a fuse element which may stand at relatively hightemperature and thus tend to damage the surrounding sleeve of fiber orthe like, and to avoid the efiects of corona, I provide a corona andheat radiating element adjacent the fuse element which, by conductingthe heat to a rather extended surface, reduces the intensity to a pointwhere temperature will not build up dangerously and, due to its shape,avoids corona discharge of high voltages.

T is same structure of a thermoshield surface in the preferredembodiment of my invention has another very important function, namely,that of providing a spark gap in shunt with the fusible element wherebyhigh voltage disturbances of the type designated as surges or steep wavefront impulses or impulse voltages may pass through the device withouttraversing the fusible element. This surge protection feature isapplicable not only to air type fuses but also to liquid type fuses, or,in fact, any form of fuse subject to disturbances of the aforesaid type.

The principal object of my invention is to provide a simple, efficient,low-current fuse link, which may be readily and economicallymanufactured, and which will have an independent, accurate,predetermined time-current characteristic, and sufficient mechanicalstrength to make it universally suitable for application in commerciallyavailable high-tension fuse devices.

An important object of my invention is to provide for applying apredetermined non-cumulative tension to a fusible member, regardless ofthe manner in which it is installed for operation.

Another object of my invention is to provide for prestressing a fuselink prior to installation in an electrical circuit to an extent whichis generally greater than it would later be stressed under normaloperating conditions by the mounting in which it is placed; and to basesaid prestressing upon the peculiarly advantageous relationship whichwill be shown to exist between the minimum fusing current and theimposed stress, so that slight deviations from the selected stress willnot materially alter the fusing characetristic of the link, yetretaining a reasonable factor of safety between the ultimate tensilestrength of the link and the tensile load.

Another important object of my invention is to provide for shielding theinner surface of a fuse receptacle or tube from the heat which wouldotherwise be applied thereto from the fuse member mounted therein.

A further object of my invention is to provide for mounting a fuse underdifferent operating conditions, depending upon the type of mountingreceptacle in which it is to be applied.

Another object of my invention is to provide a fusible element having agreatly increased ability to withstand steep wave front, transientcurrents of great magnitude but very short duration, as for example,surges produced in overhead distribution lines by lightning.

Other objects of my invention will in part be obvious and in part appearhereinafter.

My invention, accordingly, is disclosed in the embodiments hereof shownin the accompanying drawings and comprises the features of construction,combination of elements and arrangement of parts which will beexemplified in the constructions hereinafter set forth and the scope ofthe application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of myinvention, reference may be had to the following detailed description,taken in connection with the accompanying drawings, in which:

Figure 1 is a view in side elevation showing a fuse link constructed inaccordance with my invention and assembled for installation in a fusereceptacle;

Figure 2 is a sectional view showing the details of construction of aDrestressed fuse link provided with a shield;

Figure 2A is a sectional view showing the construction of the shield;

Figures 2B and 20 show the manner in which the prestressing spring maybe attached to the lower fuse link terminal fitting, Figure 20 beingenlarged;

Figure 3 is a view in side elevation of a fuse installed in a mountingdevice;

Figures 4, 5, 6 and 7 are sectional views illustrating the principle ofoperation of the prestressed fuse link;

Figures 8, 9, 10, 11 and 12 are views showing different types of fuselink adapters;

Figures 13 and 14 are views of a type of connector which may be used forapplying the fuse link shown in Figures 1 and 2 to a power line;

Figure 15 is a view in side elevation of a fuse device applied, usingthe connector shown in Figures 13 and 14;

Figures 16, 1'7, 18, 19, 20 and 21 are views showing various forms ofapplication of my novel fuse to different types of fuse mounting;

Figure 22 is a longitudinal section through the upper end of a liquidfilled fuse embodying my invention;

Figure 23 is a fragmentary front elevation of the fuse and terminalassembly before mounting the same in the device of Figure 22;

Figure 24 is an edge view of the assembly shown in Figure 23;

Figure 25 is a top plan view of the terminal employed in the device ofFigure 22;

Figure 26 is a sectional view, similar to Figure 2, showing theradiation shield applied to a fuse having both strain and fuse elements;and

Figures 2'? and 28 show a number of curves which demonstrate certaincharacteristics possessed by fuses constructed in accordance with myinvention.

According to my invention I have provided for prestressing in anon-cumulative manner the tension wire forming the fusible element of afuse. The internal stress which is applied on assembly to the fuseelement is usually greater than any stress which will ordinarily beapplied to the link later, on installation. As a result, regardless ofthe type of fuse mounting, or the different tensions which may beexternally applied by different operators or linemen, substantially thesame tension will always be applied to the fusible element. As a result,the time of operation of a particular link as a function of blowingcurrent will remain substantially fixed, since the same or substantiallythe same stress will always be applied thereto. For this reason, under agiven overload, the fuse will operate within a predetermined timeinterval which will always be substantially independent of the type ormanner of installation.

In order to prevent charring of the inside of the tube or sleeve ofinsulation which normally is used to house the fuse element and to avoidthe effects of corona, I have provided a cylindrical shield which isfixedly secured to one of the terminals of the fuse link and extendsalong the fuse link, substantially concentric therewith. The shield isformed of a material having a relatively high heat conductivity, such ascopper or aluminum, and as a result the heat which would normally beradiated or conducted to the inner surface of the insulating sleeve isabsorbed by the shield and conducted thereby to other metallic parts ofthe fuse assembly, with the result that there is no concentration ofheat in the vicinity of the fuse link, or charring of the insulatingtube surrounding it.

With a view to providing a universal mounting for the prestressed fuse,an adaptor has been provided having knock-out portions disposed atdifferent positions, Depending upon the type of fuse mounting, differentknock-out portions may be removed to adapt the fuse for mounting indifferent fuse receptacles which are already in use.

Referring now particularly to Fgures 1, 2 and 3 of the drawings, it willbe. observed that a fuse link 1 comprises three essential elements;first, a terminal portion 2, such as is suitable for attachment to oneelectric terminal and support; second, a fusible section or wire 3; and,third, a flexible lead and terminal portion 4 for making connection withanother electric conductor with which the link is to be connected inseries. The wire 3 is preferably a high tensile strength wire, of highmelting point, for ampere ratings of small value. Since the springtension to which it is subjected is of the order of six pounds it can beseen that a small diameter wire of soft metal alone is not suitable formy purpose. The portions 2 and 4 are preferably adjustable to meetvarious conditions of mounting, as I shall describe in detailhereinafter. The fuse link I is preferably enclosed in a housing such asthe fuse tube 5 shown in Figure 3 of the drawings, A more detaileddescription of the manner in which the fuse link I is mounted in thefuse tube 5 will be set forth hereinafter. The flexible lead of terminalportion 4 comprises a stranded copper or the like conductor, the outerend of which, as shown at 6, is tinned, to hold the strands together andwhich is provided also with a collar member 1. The collar member I isprovided with an intermediate portion 3 which is pinched or flattenedupon the body of the lead 4 and stamped with the ampere rating, asindicated at 9, and further is provided with a flared or conical wedgingcontact ID for engagement in a cooperating stationary wedging contactmember, as indicated at [2, in Figure 3.

The upper terminal member 2 comprises a cylindrical stud member l3 theouter end of which is threaded at M. The intermediate portion comprisesa flange 15 which may represent the original diameter of the stock fromwhich the stud is cut, as by a screw machine. Adjacent the flange l5there is a groove I6 and beneath the same a knurled portion H, The innerend of the stud I 3 comprises a tubular socket portion 18 into which isinserted the upper end of the fusible wire 3. In order to hold thefusible wire 3, the collapsible socket portion I8 is pinched flat uponthe corrugated or otherwise deformed ends thereof. The corrugationsassist the friction in sustaining the tension imposed on the strain wireso that full tensile strength of said wire may be developed in a shortconnection. The stud I3 is provided with a flanged head 26 the upper endof which is flanged or flared out as indicated at 21 as by a spinningoperation. When the annular seat is of greater extent than would besuitably engaged by the flange 21, a dished washer 28 is provided.

The lower end of the fusible wire 3 is secured, as illustrated, in ashield fitting 29, shown in section in Figure 2A, which comprises tworetaining parts, namely, 30 and 32. It will be observed that the lowerend of the fusible wire, 3 is gripped in the part 3i) of the shieldfitting 29. This fitting 29 therefore forms a coupling or junctionmember between the lower end of the fusible element 3 and the lead 4. Italso forms an anchorage for the tension spring 33, which has its uppercoil flattened against the flat sides of the pinched socket 30 and isprevented from disengagement by the shoulders of the flattened part ofthe socket 32, since the flattened portions of the sockets 30 and 32 areso disposed that their planes are substantially at right angles witheach other. The spring has its opposite end anchored by the lower endturn, which is collapsed to embrace the cable below the flattened collar35, which is pinched upon the flexible lead 4 at a point which permits aslight slack portion 40 in the lead 4 to permit a slight amount of lost'motion between the remainder of the lead 4 and the fitting 29.Indirectly, the spring 33 is anchored to the cap or plate 36 through themedium of the fitting 1, which has its adjacent end 31 in engagementwith the plate or cap 36. The margin of the plate or cap 36 is so formedas to center it upon the lower end of a fiber tube or sleeve 38. Theupper end of the tube 38 is securely bound to the upper terminal stud I3in axial alignment therewith and rigid for both rotary and axial motionwith respect thereto. This engagement is secured preferably by wettingthe end of the fiber tube 38, pushing it over the knurled portion I1,and then shrinking the end into the groove under the flange l5. Suchshrinkage may be facilitated by pinching.

It will further be observed that the shield fitting 29 has an integrallyformed metal radiation shield 49, Figures 2 and 2A, which is adapted tosurround the major part of the fusible wire 3 that constitutes the fuselink. The shield 49 comprises an enlarged tubular portion which isadapted to loosely surround the fusible wire 3 and to lie in axialalignment therewith but out of contact with the inner wall of the flbertube 38 in which it is contained. The small gap between the shield 49and the upper terminal I8 prevents shunting of the fuse wire 3 butpermits static or steep Wave front discharges to occur substantiallyfrom the terminal IE to the radiation shield 49 without traversing thewire 3. Thus, sharp static overloads, which might otherwise causeblowing of the fuse unnecessarily, are ineffective to cause suchoperation.

As shown in Figure 26, the wire 3 may be shunted by means of a conductor3a forming a more readily fusible element and composed preferably ofsilver, although other low resistance metals or alloys may be usedinstead. The conductor 3a may be wound in contact engagement with thesurface of the wire 3, which here is em ployed principally as a strainwire, and the shield 49 may be provided in the same manner and for thesame purpose as shown in Figure 2 of the drawings and described herein.

Referring to Figure 2B of the drawings, it will be observed that thefitting 29 has been modified by the omission of the shield 49 to formthe fitting 29b, which is otherwise identical therewith. The topconvolution of the spring 33 is flattened out to closely engage theretaining part 30, as shown in the top view of the assembly in Figure2C. The required slack in the lead 4 for the slack portion 40 isobtained by untwisting the portion of the lead that is connected to thefitting 29b. The amount of untwisting determines the amount of slackwhich should be maintained at a predetermined value for properoperation. Therefore, the ends of the slack portion 40 or the fitting29b and the collar 35 attached thereto must be prevented from rotatingrelative to each other, due either to the natural tendency of the slackportion to return to its normal position or to any external twist whichmay be applied to the other end of the lead 4. This is effected bynon-rotatively clamping the top and bottom of the spring 33 to thefitting 29b and the collar 35, respectively, which in turn are collapsedon the lead 4. It will be understood, of course, that this manner ofconstruction is also used in the connection of the spring 33 to theshield fitting 29.

When the current flow through the wire '3 becomes an appreciable amount,the heat given off thereby may be considerable, particularly as it mayaccumulate, if not otherwise dissipated. It is very important tomaintain tension upon the fuse at all times, and since the support forthe spring 33 rests upon the end of the fiber tube 38, it is necessaryto insure the life and permanency of the tube 38.

As a further result of the provision of the relatively large diametershield 49 about the relatively small diameter wire 3, the effects ofcorona are materially reduced. This is due to the fact that theeffective diameter of the wire '3 is greatly increased by the shield 48and there is consequently less ionization of the atmosphere in thevicinity of the wire 3.

In fuses constructed as shown in Figure 2 of the drawings, employing thenickel-chromium wire 3, the temperature of the fusible section may reachfrom 800 to 900 C. before the link blows. At these temperaturessuflicient he'a't may be transmitted by radiation to the surroundingfiber tube 38, during prolonged overloads approaching the minimum fusingcurrent, to injure, and possibly cause collapse of the walls of thetube. This would result in a modification of the predetermined minimumtension and a change in the characteristics of operation. The radiationshield 49 has been provided to eliminate this. As stated hereinbefore,the shield 49 is a metallic tube of good thermal conductivity, formedwith the terminal fitting 29. Either the terminal 18 or the terminal 29may have the shield 49 attached thereto. The shield '49 is preferably ofcopper, or other metal of high thermal conductivity, and it receives thedirect radiation from the wire 3 and dissipates the heat, by conduction,to the adjacent parts, and by radiation over a larger area than thatwhich would be effected by the wire 3 alone. The peak temperatures ofthe wire 3 are always attained at the midpoint of the fusible section,hence the small gap at the end of the radiation shield 49 does notmaterially alter or reduce the effectiveness of it. The dimensions ofthe tube 38, the shield 49, and the alignment of the parts, is such thatthe shield cannot come into contact with the fiber tube, and sufficientroom is provided for the free expulsion of the shield 49 and itsconnected parts upon blowing of the fuse wire 3.

The fusible wire 3 is preferably formed of a nickel-chromium alloy,secured upon the market under the trade name of Chromel A. Tests showthat this nickel-chromium wire retains considerable mechanical strengthat elevated temperatures (even at red heat), but that a rather abruptweakening occurs at temperatures which have been computed to be about800 to 900 C. The melting point of these wires is approximately 1400 C.The effect of these properties of the nickel-chromium wire is to producea certain relationship between the current flowing and the mechanicaltension, which has been utilized to render these links practicallyindependent of external mechanical forces, within certain limits. I havemade tests to determine the elfect of spring tension upon thetime-current characteristic of a link. These tests show that a directrelationship exists. For example, the current required to blow a fusewire of a diameter of 020d inch in seconds this approximates the minimumfusing current for the particular terminal arrangement employed duringthese tests), amounted to 12.5 amperes, when no tension is applied. Thecurrent, however, decreases rapidly with increased spring tension up toabout 4 pounds, which means that rupture occurs at temperatures belowthe melting point progressively approaching the critical range of from800 to 900 C., as the tension approaches 4 lbs. for this particular sizeof wire, corresponding to a current of approximately 7 amperes. Anyfurther increase in tension results in a gradual but slight decrease inthe blowing current until the ultimate strength of the wire is reached,whereupon the blowing current abruptly drops to zero. That is to say,there is a purely mechanical failure. If the link assembly contains noprovision to apply a mechanical load, it is apparent that any particularlink would have a time-current characteristic which would vary with themechanical loading. Since the time of operation of the fuse wire dependsupon the applied tension, it will be clear that the tension appliedthereto should always be maintained at the same value in order to getconsistent operation. For this purpose I have provided for prestressingthe fusible element 3.

The relationship between the time required to cause a fuse wire to blowand the current for different tensions applied to it, is illustratedgraphically in Figure 28 of the drawings. As there shown, with notension Po applied to the wire, the current Io required for blowing thewire is greater than the current, for example, I1 or 12, required toblow the fuse wire to which a tension P1 or P2, respectively, isapplied. Thus, for a given fuse wire, the ratio between blowing currentsmay be of the order of 1:2, depending upon whether the fuse wire isstressed or not.

The curves shown in Figure 2'7 illustrate the relationshipbetween thetension applied to fuse links or wires of several different currentratings and the current required to blow them in 100 seconds. With notension applied to the link or wire the blowing current is approximatelytwice that required when a tension P1, equal, for example, to about 4lbs., is applied, which brings the blowing currents below and to theright of the knees of the various curves. It will be observed that thecurves are substantially parallel with the x-axis for a considerablepart thereof, indicating that in the fiat portion of any one of thecurves the fusing current for a given time will be substantially thesame, regardless of the tension applied greater than the, minimumtension required to enter the region to the right of the knee of thecurve. If the tension P2 which is applied externally in mounting thefuse link is of the order of to 12 lbs., the current I2 required to fusethe 10 ampere link will be substantially the same as the current I1required to fuse it if an external tension no greater than P1, forexample, 4 lbs. as assumed, were applied. It will thus be apparent thata fuse link which is prestressed to the required tension will alwaysblow according to its current-time rating although it may be sub jectedto widely varying tension conditions, due to different types and mannersof mounting it for operation in a fuse receptacle or otherwise.

It will be observed that the tension at which even the lowest rated fuselink will break or fail mechanically is considerably beyond the tensionP2 to which it will ordinarily be subjected. Thus for even the smallestsize of fuse link, what may be termed a handling strength of about 20lbs. is available. Such a relationship would not exist and the blowingcurrent would not be so constant over the wide tension range if the linkwere not prestressed to bring it into this operating region.

In order to demonstrate the manner in which the fusible element isprestressed, reference may be had particularly to Figure 3 of thedrawings. In Figure .3 it will be observed that the fuse link I hasapplied thereto an. external force derived, for example, from thecut-out spring 50, as in the well known Schweitzer & Conrad cutouts, butthe construction of the fuse link I is such that the stress applied bythe spring 53 does not add cumulatively to the seven pound tension ofthe spring 33 embodied in the fuse link itself. This will be apparentwhen the detailed construction of these fuses is considered. Any tensionupon the flexible lead wire 4 in excess of the tension of the spring 33will shift the abutting portion 31 from the cap or plate 36 to take thereaction of the spring 33 off of the fiber tube 38 and to place itagainst the endof the collar 35 which is attached fixedly to the lead 4.Thereupon the spring 33 is further extended or expanded to take up theslack in that portion 40 of the flexible lead 4 which lies between thecollar 35 and the socket 32, and thereupon add to the tension upon thefuse wire 3 the difference between the tension of the spring 33' andthat added by the mounting. That is to say, assume that the pull uponthe flexible lead 4 produced by the spring 50 in Figure 3 is 12 lbs, andthat the initial stressing of the spring 33 is '7 lbs. The tension uponthewire 3 is not the sum of land 12 lbs., but is merely 12 lbs., sincethe spring 33 and the section 40 of the lead 4 are mechanicallyconnected in parallel. The load is thereby divided, so thatapproximately 8 lbs. is transmitted through the spring 33 and 4 lbs.through the cable section 40. This relieves the joint between the socket32 and the pinched end of the cable 40 from the full mechanical load.The great virtue of this construction resides in the fact that theminimum loading of the fuse link is fixed by the spring 33 and theloading produced by the mounting does not add thereto unless it isgreater than the initial spring tension of the spring 33. Moreover,because of the provision of the spring 33, the link assembly is capableof more readily interrupting low current arcs than has been possiblewith the constructions of the prior art. By means of the foregoingdescribed construction, a series of lowcurrent links, of ratings from 1to 10 amperes, may be provided in which, by proper coordination of theminimum and the maximum values of tension to be imposed on the fusiblesection, and the mechanical properties of said section as related to itsfusing characteristics, the desired results may be obtained. These fusesembody time-current characteristics which are essentially the same,regardless of the type of cut-out or mounting in which they are applied.

For a further description of the character of the predetermined springtension, reference may now be had to Figure 4 of the drawings, wherein aspring 53 is shown as anchored at 54 upon the end of the fiber tube 38,the additional spring loading of the mounting being indicated at 55.Here, if it be assumed that the spring 53 imposes a minimum tension of,for example, 7 lbs., any tension or load which is imposed by themounting through the spring, as indicated at 55, produces an additiveeffect. That is to say, whenever the tension of the mounting is appliedas to the spring 55, it will be added to the tension of the spring 53,and thereby there will be a tendency to alter the time-currentcharacteristics of the fusible link 3, depending upon the mounting inwhich the link is placed. By comparison with the construction shown inFigure 5 of the drawings, it will be seen that the additional load 55 ofthe mounting tends merely to take up the reaction of the spring 33 uponthe end of the fiber tube 38, and unless the load as indicated at 55 isin excess of the reaction of the spring 33, no additional tension willbe imposed upon the link 3'. As shown in Figure 6 of the drawings, thespring 33 alone may serve as the connection between the flexible lead 4and the terminal of the fusible link 3. That is to say, the shuntportion 40 is not essential where the spring has sufficientconductivity.

The spring which applies a predetermined tension to the link 3 need notbe a tension spring,

- but may be in compression, as shown in Figure '7 of the drawings. Thecompression spring 55 is here disposed between a head 51 on the movableterminal 58 and. a flange 59 of the yoke or tube 60, to which theflexible lead 4 is connected. A feature of the constructions indicatedin Figures 6 and 7, as compared with that of Figure 5, is to be noted inthat when no shackle or limit to the motion of the spring 33 or 56 isprovided, the more stressed spring 55 and the less stressed spring 33 or56 will strike a balance of displacement when the tension of the link 3will be something less than that of the spring 55 and something morethan that of the spring 33 or 56. This is all within the concept ofnon-cumulative loading. When a compression spring is employed, thecontacting of the convolutions may serve as a limit or shackle.

In order to adapt fuse links of my invention for mounting in variousdevices such as are now mployed, I have provided the fittings oraccessories illustrated in Figures 8 to 12, inclusive.

In Figures 8, 9, and 11, a fitting 62 is illustrated, preferably made ofa drawn tubular piece of metal such as a copper tube, having a threadedportion 63 at the lower end for cooperating with the threaded stud I4 ofthe fuse shown in Figure 2. The upper end of the fitting is expanded orspun out to form a conical head 21 substantially identical with the head21 shown in Figure 2. An intermediate flattened portion 64 is formed bypinching the walls of the tube together. A tongue 85 is sheared out ofthe upper end of the flattened metal portion 54, so that the head 21 maybe broken off and the tongue 65 removed, to leave a notch 06, as shownin Figure 9, when a mounting around a bolt or pin is required forconnecting the link at its upper end to a corresponding terminal. Aconical washer 28, as shown in Figures 2 and 10, may be employed, wherethe head is retained for mounting upon an annular seat, as will bedescribed hereinafter.

The terminal 67 shown in Figures 10 and 12 is similar to that shown inFigure 8, except that in this instance a tongue such as 68 is strucklaterally in the flattened portion 64, so that when the head is brokenoff and the tongue broken out, the terminal appears as shown in Figure12, with the notch 69 in the side edge of the flattened portion 64. Thisadapts the terminal for connection in certain binding post arrangementsin mountings now in use. The use of partially sheared, portions, whichmight be termed knockouts, permits the utilization of the metal forelectrical and heat conductivity, with ready removability. Bothknock-outs may be embodied in the same terminal portion 60.

In Figures 13, 14 and 15, I have shown a form of mounting in which thedevice of Figure l is adapted to be employed as a complete operativefuse device in connecting a house drop conductor to a line ordistribution conductor. This device comprises a connector 14 adapted tomake connection with a continuous conductor such as 15, as shown inFigures 14 and 15, The secondary distribution conductors I5, '15 and TI,shown in Figure 15. are supported upon a secondary rack I8. providingsuitable insulators for each conductor, the rack being mounted upon apole '19 or the like. The drop 80 comprises, in this case, pair ofconcentric conductors having leads 82 and 83 which are adapted to beconnected to the secondary distribution conductors I and TI. Theconcentric pair forming the drop 80 includes a support ng strand. whichmay be a suitable ire cable 84, anchored upon the pole I9 through aninsulating eye 85 having a threaded shank screwed into the pole.

The connector 74 comprises a U-shaped body, the base 35 of which ishexagonal in form and the parallel arms of which are threaded asindicated at 8! to receive a clamping nut 88. A transverse bar 89,having a shank 90 extending ins de of the nut 8, of a w dth tosubstantially fill the slot 92, so that when the nut 88 is screwed downto clamp the bar 89 upon the conductor IS, the arm 01 will not be ableto escape from the nut 88. The shank 00 has the ed es the eof rivetedover the top ed e of-the nut 88, so that the bar 89 and nut 83 willremain t ether. even. when they are removed from the fitting M to admitt e continuous secondary conductor 1'5. The conductor is preferablyinsulated, but it has the insulation removed in order to accommodate theclamp 14. The clamp I4 has a threaded opening axially through the bottomhexagonal portion 86 to receive the shank I4 of the upper terminal I3 ofthe link shown in Figures l and 2 of the drawings. The flange I5 isscrewed up tightly against the bottom face of the hexagonal portion 86to make good electrical connection and to support the link with thefiber tube 38 in horizontal position.

The flexible lead 4 is connected to the corresponding conductor of thedrop 80, as shown in Figure 15. Within the fiber tube 38 is disposedspring 33 and in the event of overload in the circuit including theconductors 82 and 83, the fusible link operates and the lower terminal,to which the spring 33 is attached, retracts the movable terminal suchas 29. The spring recoil. with the addition of the gases freed or formedupon blowing of the fuse, expels the terminal 29 from the tube andthrows the wire 82, for example, with the connected link 4, to the rightas viewed in Figure 15, into the clear. The conductors 82 and 83 may beso disposed and formed as to facilitate this action. From this style ofmounting it can be seen that the fuse link is a complete fuse devicewithin itself having its own fiber expulsion tube and spring loadedfusible element, capable of maintaining its predeterminedcharacteristics quite independently of any ad from an additional fusetube or the mounting in which it may be disposed.

The general purpose to which this form of fuse link may be applied isillustrated in Figures 16 to 21 of the drawings, inclusive, as well asin Figure 3, as has previously been mentioned.v The device shown inFigure 3 comprises a standard device on the market, manufactured by myassignee, and is designated as the S & C ejector cutout (see Patent No.1,818,382). It comprises a tubular porcelain or like insulating housing93 within which are mounted annular terminals (not shown) for makingconnection with the corresponding annular terminals on the fuse tube 94.The lower ferrule on the fuse tube 94 carries an arm 96 with a conicalwedge-like socket I2 to receive the conical wedge-like member I0 shownin Figure l of the drawings, the lead 4 below the member I0 being cutoff when the device is installed. The upper end of the unit I has thethreaded stud I4 threaded into a threaded.

socket 91 which, in turn, is connected to the spring 50. Upon operationof the device under excessive current flow the spring 50 pulls the upperterminal I3. with the connected fiber tube 38. upwardly, and the spring33 throws the lower terminal fitting 29 downwardly. At the same time,the gases of the arc tend to assist in expulsion of the lower terminal.the spring 33, the flexible lead portion 00, and the plate 35,

In Figure 16 I have shown the link of my invention as employed in acutout box I00 hav ng a lid IN. The fuse tube I02 carried upon the lidmember and the ferrules I03 and I04, are provided with pro ectingcontact springs formed of pairs of wires for engaging stationary flatstuds I05 and I06 mounted on the bottom of the box member I00. The fusetube I02 employs a retractile sprin such as that ind cated at 50 inFigure 3 of the drawings, with a flexible lead I01 connectin thethreaded socket I00 and the threaded plug I09 which closes the upper endof the ferrule I03. The threaded socket I08 receives the threaded studof the upper terminal member I3 and the flexible lead 4 is brought outof the lower open end of the tube and brought back to a clamp whatdifferent from that shown in Figure 16. In

this device the lid I I I, which carries the fuse tube H2, is held inclosed position on the box H3 by the integrity of the link I in the fusetube H2.

The fuse tube II 2 has an upper ferrule II 4 with a threaded cap I I5for clamping upon an annular seat the button heads such as shown inFigures 1 and 2 of the drawings to make connection with the upperterminal. The ferrule H4 is fastened to the door III. The fuse, tube H2is mounted in a fitting H6 with respect to which the fuse tube may havea sliding motion under the influence of the spring IZI to move the fusetube downwardly to disengage the pin II! from the latch spring III!which connects with the upper stationary terminal I I9. The lower end ofthe fuse tube bears upon a pivoted link I20piv-.

oted at I22 toithe fitting H6. The lower end of the fuse tube H2 ismounted in a stationary bracket I23 mounted upon the door I I I. Acamshaped clutch jaw I24 grips the lower end of the flexible lead 4against the corresponding jaw on the link I20. The tendency of thespring in com.- pression is to stress the fuse tube H2 down against thelink I20 and this reaction is taken up by the tension in the flexiblelead 4 and thence in the entire link. Upon melting of the fusibleelement the fuse tube H2 drops down, as the link I is no longersustained by tension of the in the box. The fuse tube I32 has an upperferrule with athreaded cap member I 35 an annular seat for clamping thebutton heads such as shown in Figures 1 and 2 of the drawings to makeconnection with the upper ferrule. At the lower end the flexible lead 4is led out through the lower end of the open tube, as indicated at I36,and the end of the lead is brought under the annular knurled nut I31 andthere clamped to the surface of the lower ferrule. In this mountingthere is no additional spring tension to that which is imposed by thespring 33 within the inner fiber tube 38 of the link. The operation ofthe device is substantially the same as heretofore described. that is tosay. the predetermined tension of the spring 33 acting upon the fusibleelement causes the same to be parted when the proper current value isreached, the resultant parting assisting in expellingthe flexible leadand the lower terminal and connected parts.

Obviously, in any of these mountings, if the current flow is so heavy asto result in a violent blowing of the fuse, the inner tube or sleeve,which is the sleeve 38 of the link, may be shattered, but even in suchoperation the inner surface of the main or outer sleeve or tube I02, H2or I32 is protected in large measure. The outer sleeve is usually madeof fiber which, when the are is heavy, evolves a beneficial gas and alsocleans itself.

In Figure 19 I have indicated a mounting of the fuse tube I45 to securea dropout effect of the said fuse tube I45 from the mounting. Thismounting comprises an upper stationary bracket I46 comprising a hoodcontaining suitable contacts and including a spring mounted pin I4!which is adapted to be engaged by the hook I48 formed on the movablesleeve I49 of the upper ferrule I50. A compression spring between thesleeve I49 and the stationary ferrule member I50 and housed in sleeveI49 tends to throw the sleeve I49 and hook I48 upwardly. The sleeve I49has a threaded cap I5I for clamping the button head of a suitable springmounting. A tension spring I52, shunted by a suitable flexible conductorI53, carries at its lower end a threaded coupling I54, and the stud I3of Figure 2 is threaded into said fitting I54, whereby the upper portionof the link I is mounted within the lower end of the fuse tube I 45. Theflexible lead 4 is carried down to the lower end of the extension on theferrule I55 and connected under a binding post I56. When the fusiblelink melts or yields, the spring I52 pulls the stud and tube 38upwardly, releas-.

ing the sleeve I49 and permitting the hook I48 to travel upwardly anddetach itself from the pin I41. Thereupon the force of the springcontacts which bear upon the sleeve I49, and the force of gravity, throwthe fuse sleeve I45 in a clockwise direction about the trunnion I51,taking the fuse tube I 45 out of the circuit.

Another form of fuse mounting is shown in Figure 20 of the drawings. Thefuse tube I60 in this structure has an upper ferrule I6I and a lowerferrule I62. The upper ferrule I6I has an opening through the samepermitting the sleeve 38 of my link I to be passed therethrough,allowing the button head 2'! to project. A finger I63 projects upwardlyfrom the upper ferrule I6I and is designed to pass through a pair ofspring rods I64 forming the upper terminal. These spring rods pressdownwardly, both to make contact with the button head 2'! and to throwthe fuse tube I00 into open position when the fuse element of my linkmelts. The lower ferrule I 62 has an arm I 61 pivoted to a bell cranklever I 68, one end of the lever being held against the lower end of thefuse tube I60 by the flexible lead 4, which is fastened under thebinding post I65. The bell crank lever I68 has a hook about the trunnionI69, which trunnion is mounted on the lower stationary terminal of themounting. The downward thrust of the spring rod I64 is sustained by thelink I, which holds the arm I19 of the bell crank lever I68 against thelower end of the fuse tube I60. When the link I is ruptured by meltingof the fusible element the downward thrust of the spring rod I64 and theweight of the fuse tube I50 tend to cause a rotation of the bell cranklever I 68 in a clockwise direction about the trunnion I69. This actionpulls the flexible lead 4 outwardly in the tube I60. At the same timethe fuse tube I60 descends and, as the button head escapes from underthe hump I I0 in the spring rod I64, the fuse tube I60 drops out of thecircuit.

Still another type of fuse mounting is shown in Figure of the drawings.In this figure I have shown the link of my invention employed in amounting having a fuse tube III, the upper ferrule of which has aknurled cap I12 and an annular seat for receiving the button head suchas is shown in Figures 1 and 2 of the drawings. The

fiexible lead A, in this instance, is attached by a clasp I'IS attachedto a leaf spring I14 anchored at I75 to the lower ferrule I'IG. Uponmelting of the fuse the leaf spring I 54 fiips the lead wire 4 andconnected lower terminal out of the lower end of the fuse trbe ill. Inthis construction the leaf spring H4 supplies spring tension for anylink which is mounted in the device. The link of my invention isinterchangeable with the original fuse link supplied in connection withthe mounting shown in Figure 21. In this construction the springbrackets for mounting the fuse tube are supported upon an insulatingmember II'I which, in turn, is adjustably mountedvupon a cross arm I78by a suitable metallic pin clamp and bracket.

From the foregoing illustrations it will be observed that the fuse linkof my invention is interchangeable and applicable in a wide variety ofmountings which now employ fuse links constructed in accordance with theteachings of the prior art. Th fuse link of my invention, havingpredetermined spring tension independently of the mounting, and being soarranged that the spring load or gravity load of the mounting is exertedagainst the reaction of the spring 33, will maintain a time-currentcharacteristic of a predetermined nature with utmost fidelity,independently of the particular mounting in which it is employed. Theabove illustrated mountings are but typical examples of mountings inwhich the fuse of my invention may be used.

From the foregoing it will also be apparent that I have provided a fuselink suitable for em ployment in a Wide variety of mountings, and inwhich there is a predetermined spring tension to control th time-currentrelationship of the fusible element according to a desired mode ofoperation. This predetermined spring tension also assists in parting thenickel-chromium or the like wire when th current value is such as tocause the wire to lose its mechanical strength. By cordinating thespring tension with the cross section of the wire, a very definitetime-current relationship and response is obtainable.

Insofar as I am aware, it is broadly new to employ the radiation shield19 to protect the internal surface of the surrounding tube or the mainfuse tube from injury by radiation of heat from the fuse wire,particularly when this fuse wire operates at a fairly high temperaturefor a considerable period of time before it fuses. Moreover, a fuseconstructed in accordance with my invention employs the feature ofnon-additive spring tension or loading in the mounting. That is to say,the load which is imposed upon the link of my invention by conventionalmountings does not necessarily increase the tension upon the fusibleelement, because the loading of the mounting is applied in firstovercoming the reaction of the spring 33 before further tension isapplied to the fusible element.

Still another novel feature of my invention as described hereinbefore isthe provision of various types of attachments and fittings for makingthe fuse applicable to a wide variety of mountings. A particularlyimportant feature is the employment of the threaded stud withinterchangeable terminal parts, whereby the link may be applied to awide variety of terminal fittings. With such arrangement the heatgenerated in the fusible member may be more readily dissipated.

The tube 38 is preferably of fiber which evolves gases by destructivedistillation produced by the heat of the are, which gases are beneficialin extinguishing the arc. The tube may be treated end and forming aclosure.

with or lined with material which promotes the gas evolution.

The invention is not to be limited to the use of a high tensile strengthwire for the fusible element, as the spring tension will assist theparting of any fuse conductor when subjected to mechanical stress andheat. a The non-cumulative loading may be employed where a silverconductor 3a and a strain wire 3, as shown in Figure 25, form thefusible element for certain advantages-such as non-accumulativetensioning of the strain wire, which preserves the margin of safetyagainst mechanical breakage, rapid separation of the terminals and thelike. but the beneficial effect upon the time-current characteristic insuch cases would be slight since the blowing time of the strain wireafter the fusing of the main fusible element is usually negligible.

It will be observed that the link of my invention is a complete fusedevice within itself, and may be so employed. as shown, for example, inFigure 15 of th drawings. In this form it is suitable for lowervoltages, such as 110 or 220 volts. Obviously, by changing theproportion of parts the voltages may be higher, depending upon theservice which is required. It will be noted that the fuse shown inFigure 15 of the drawings may omit the spring where the fuse rating isgreat enough to provide the expulsive functioning.

The surge protecting feature and radiation shield of my invention areapplicable to fuses generally. In Figures 22 to 25 I have illustratedits employment in a liquid filled fuse of the type illustrated inFigures 1 to 4 of Patent No. 1,743,322. This type of fuse is for smallampere capacity, but applicable to any desired voltage. The fuseillustrated in Figure 22 comprises a glass sleeve I carrying a ferruleI92 at the lower At its upper end there is mounted a ferrule I93 whichis provided with an open top normally closed by a vent cap I94 suitablycemented or otherwise secured over the opening and adapted to bereleased by internal pressure generated within the closed fuse housingwhen the fusible element is blown. The ferrule I93 has a cylindricalbore I95 at its upper end terminating in a shoulder I95. Within the boreI95 is disposed an S-shaped terminal member I9! made of fiat springstock, the cylindrical portions of which bear against the bore I95 andthe edge portions of which bear against the shoulder I96. The transversecentral portion I98 forms a diametrical bridge to which is attached theflattened portion I99 of the upper fuse terminal member 290. The upperfuse terminal member as shown in Figures 23 and 24 comprises a piece oftubing of copper or other good conducting metal in the upper part ofwhich there is disposed the eye 202 of the fusible wire 203. The upperend of the tube is flattened to produce the flat terminal portion I99and also to grip the said eye 202 of the-fusible element. The fusibleelement is preferably a length of nickel chromium wire with the endsformed into the upper eye 202 and the lower eye 204 by bend ing the endinto a loop and Welding of the end to the shank of the wire. Theunflattened portion of the tube 205 embraces loosely the main bodyportion of the wire 203 and lies out of contact with the same. A hole200 is preferably formed in said unfiattened or shield portion 205 tofacilitate the drainage of liquid from the tube, which it may enterduring shipment or handling prior to installation in the verticalposition. This is important, since the time-currentcharacteristics-would be changed by the presence of a liquid coolingmedium in direct contact with the wire.

The flattened terminal portion I99 is provided with a hole 201 forriveting said terminal portion I99 as by the rivet 208 to the bridgeportion I98 of the terminal member I91.

The upper end of the flattened portion is provided with a hole 299 bywhich the spring 2I0 may be tensioned in the assembly of the fuse. Saidextending upper end may be cut olf or bent over after the rivet 208 isin place.

The lower terminal for the fusible element comprises a tube of copperor-other metal of suitable conductivity flattened upon the lower eye204. This lower terminal 2I2 comprises an anchoring portion 2I3 at itslower end having the screw hole 2M and cross notch 2I5 for theattachment of the spring anchor at the upper end of spring 2 I 0.

Intermediate the portions 2I2 and 2I3 I provide means for supporting theliquid director 2 I B. The liquid director 2I6 has a cylindrical groove2|! formed on its inner periphery. A thin strip of spring metal shown inextended form at H8 in Figure 23 is passed through the tube of which thelower terminal H2 is composed before the same is flattened. The ends ofthe strip 2I8 ar I then bent into an S-shape similar to the terminal l9!as indicated at 2| 8' on Figure 24, and

the spring arms expand into the groove 2I7 of the liquid director I6 andhold the liquid director ists between the lower end of the shieldportion 205 and the upper end of the terminal member 2 I 2 providingthereby a surge or spark gap across which high potential surges orsimilar disturbances tend readily to pass without causing blowing of thefuse wire 2'03.

The fuse housing is filled with liquid to substantially the level of thetop of the liquid director 2 I 6 at normal room temperatures. An arcingchamber 2I9 formed of a short tube of fiber or of suitable insulatingmaterial of fibrous character, which may be impregnated with a syntheticresin, is disposed loosely about the fuse assembly. This tube 2I9 restsat its lower end on or substantially on the liquid director 2I6 and atits upper end is slotted to grip opposite 1 sidesof the bridge memberI98, as parent from Figures 22 and 25.

This tube confines the products of arcing when the fuse initially blows,and tends to cause the discharge of the metallic vapors and othergaseous products endwise towards the open end of the ferrule I93. Thecap I94 is readily removed by blowing of any appreciable violence, andthe will be approducts of the are are thereby expelled in an orderlymanner. Also, since the present fuse is of relatively small bore thearcing chamber formed by the shell 2I9 tends to save the upper end ofthe glass tube from the heat of the initial are, particularly before thearc extinguishing liquid is projected into the space occupied by thearc. I

In operation of the device the current normally flows between the lowerterminal 2I2 and the upper terminal portion 200. Any heat which isradiated from the fusible section tends to be distributed by the shieldportion 205 and is radiated and conducted therefrom to adjacentconducting parts. The shell 2| 9 tends to screen the upper end of theglass tube from direct radiation of heat.

In the event of a steep wave front disturbance of the type termed asurge arising on the circuit including the use in Figure 22 the tendencyof the same is not to follow the fusible wire 203 but to spill acrossthe gap before the Wire 203 has been fused.

Upon a relatively low overload the wire 203 is parted by the springtension and weakening of the wire and an arc is formed with resultantmotion downwardly of the terminal 2I2 and liquid director 2I6, wherebyliquid is projected into the arc space and if the pressure rises to thepredetermined value for which the cap I94 is designed to be released thegases and vapors will be expelled out of the open end. a

On more violent blowing the vaporization of the fuse wire and theevolution of gases by the arc may produce pressures violent enough toexpel the upper terminal I91 and connected 'mem her 200. The resultingflow of arc extinguishing liquid into the arc space and deioniza'tion ofthe arc results'in extinction of the same. This structure obviously iscapable of modification and variation within the above teaching.

Since certain further modifications may be made in the foregoingconstructions, and different embodiments of the invention may be madewithout departing from the scope thereof, it is intended that allmatters set forth in the foregoing description and shown in theaccompanying drawings shall be interpreted as illustrative, and not in alimiting sense.

I claim as my invention:

1. In combination, a stud member havinga threaded end, an intermediateportion, and a tubular portion on its opposite end, a fusible elementone end of which is disposed insaidtubu lar portion, which tubularportion is compressed upon said one end, a flexible lead, a tubularcoupling member having one end compressed upon said flexible lead andthe other end compressed upon the other end of the fusible element, atube of insulation surrounding said element, one end of the tubeengaging said intermediate portion, and a spring for tensioning thefusible element interconnecting said coupling member and said tube, thereaction of said spring being taken up on said tube as a compressionmember.

2. In combination, a terminal member comprising a threaded stud, anintermediate portion and a fuse coupling portion, a fusible elementengaged by said coupling portion, a flexible lead, a junction memberjoining the end of the lead and the fusible element, an insulatingsleeve secured to said intermediate portion and surrounding saidelement, an anchor member engaging said sleeve, 9. spring anchored tosaid junction memher and to said flexible lead, and means connectingsaid flexible lead to said anchor member.

3. In combination, a fusible element, a first terminal for said elementhaving coupling means, a second terminal for said element, a tube of. insulation resting against and being closed by said first terminal, anchormeans engaging, the tube, a spring connecting said second terminal andsaid anchor-means to place the tube in compression and the element undertension, andan external lead connected to said spring anchor;

4. In combination, a fusible element, a first terminal for said element,a second terminal for said element, a tube of insulation fixed at one.end to said first terminal, anchor means engaging the free end of thetube, a spring connecting the anchor means and the second terminal toplace the tube under compression and the element under tension, and aconductor anchored to said anchor means, whereby tension on theconductor is ineffective to increase the tension on the element unlessitis great enough to overcome the stress of the spring.

5. In combination, a fusible element, a first terminal for said element,a second terminal for said element, a tube of insulation fixed at oneend to said first terminal, anchor means engaging the free end of thetube, a spring connecting the anchor means and the second terminal toplace the tube under compression and the element under tension, and aconductor anchored to said anchor means whereby tension on the conductoris ineffective to increase the tension on the element unless it is greatenough to overcome the stress of the spring, a portion of said conductorforming an electrical shunt of said spring.

6. In combination, a fusible element, a first terminal forsaid element,a second terminal for said element, a tube of insulation having saidfirst terminal mounted at one end, said tube extending over said elementand said second terminal, a spring-anchor plate engaging the free end ofthe tube, a flexible lead extending through said plate and joining saidsecond terminal, a spring within the tube connecting-spaced parts of theflexible lead, and means on the lead bearing against the outside of thespring anchor plate to transmit the tension of the spring to said plate.

'7. In combination, a fusible element, a first terminal for saidelement, a second terminal for said element, a tube of insulation havingsaid first terminal mounted at one end; said tube extending over saidelement and said second terminal, a spring anchor plate engaging thefree end of the tube, a flexible lead extending through said plate andjoining said second terminal; a spring within the tube connecting spacedparts of the flexible lead, and means on the lead bearing against theoutside of the spring anchor plate to transmit the tension of the springto said plate, said means comprising a tubular member compressed uponthe lead and having a flared wedge portion for wedging engagement with astationary cooperating contact.

8. As an article of manufacture, a self-contained fuse link, comprisinga continuous conductor having terminal portions, a fusible elementintermediate said terminal portions, means for tensioning said fusibleelement comprising a spring connected at one end to the first end of theelement and connected at its other end to an intermediate part of saidconductor, and means for taking up the reaction of the spring.comprising a strut connected at one end to the other end of theelementand at itsother end to said intermediate part of the conductor.

9. As an article of manufacture, a self-contained fuse link comprising acontinuous composite conductor adapted to be mounted in an expulsiontube, said link having a, mounting terminal at the first end thereof andhaving a flexible lead for expulsion from the expulsion tube ending in asecond terminal for the link at the second end thereof, said link havinga fusible portion, the first end of said portion being connected to saidfirst terminal, the flexible lead being connected to the second end ofsaid fusible portion, and means for'holding the fuse link under'tensionindependently of the attachment or nonattachment of said terminals,

10. The combination of claim 9 wherein said means comprises a coilspring exerting-a tension stress on the fusible portion, and a tubesurrounding the fusible portion and taking upon one end thereof thereaction of said spring, whereby a pull exerted on the flexible leadwill oppose the reaction of the spring upon the tube.

11. A terminal for a fuse or the like, comprising a head, a shank, saidshank having a portion thereof partially severed transversely butmechanically and electrically in contact with the remainder whereby itserves as an electrical and heat conducting portion but may be removedto provide an opening to facilitate clamping by a binding post.

12.. A fuse link comprising a fusible element, an insulating tubesurrounding said fusible element, a first terminal member for theelement, a second terminal member for the element, said members havingportions to connect thereto the ends of the element, a flexible leadconnected to the second member, a metal radiation and corona shieldforming an extension of one of said members and covering substantiallythe full free length of said element and spaced therefrom with an airdielectric therebetween.

13. A fuse link comprising a fuse element, a first terminal member forthe element, a, second terminal member for the element, said membershaving socket portions pinched upon the ends of the element, a flexiblelead connected to the second member, a metal radiation and corona shieldforming an extension of one of said members and covering substantiallythe full free length of said element, and a tubular insulating sleevesupported coaxially with said shield but out of contact with the same.

14. A fuse link comprising a fuse element, a stud forming a first fuseterminal for said element, 9. tube of insulation having one end boundupon said stud in axial alignment, said element being anchored in theend of the stud inside the tube, a second fuse terminal for said elementdisposed in said tube and secured to the end of said element, saidlatter terminal having a tubular radiation and corona shield extendingloosely about but out of contact with the element over substantially itsfull length, and a flexible lead for said second terminal.

15. A fuse link comprising a fuse element, a stud forming a first fuseterminal for said element, a tube of insulation having one end boundupon said stud in axial alignment, said element being anchored in theend of the stud inside the tube, a second fuse terminal for said elementdisposed in said tube and secured to the end of said element, saidlatter terminal having a tubular radiation and corona shield extendingloosely about but out of contact with the element over substantially itsfull length, a flexible lead for said second terminal, and a springbearing against the end of the tube and tensioning the element.

16.. In a fuse, a fitting comprising a terminal and radiation shieldmember consisting of a tubular portion adapted to embrace loosely a fusewire, an intermidate tubular portion of smaller diameter adapted to bepinched upon the end of a fuse wire, and a socket adapted to receive theend of a flexible copper lead and to be pinched thereupon.

17. In a fuse, a fitting comprising a terminal and radiation shieldmember consisting of a tubular portion adapted to embrace loosely a fusewire, an intermediate tubular portion of smaller diameter adapted to bepinched upon the end of a fusewire, and a socket adapted to receive theend of a flexible copper lead and to be pinched thereupon, saidintermediate portion and socket being flattened in planes disposedsubstantially at right angles to each other, and a tension spring havingan end coilanchoredupon the shoulder formed between said two flattenedportions.

18. In a fuselink, a pair of fuse terminals, a fusible sectionconnecting said terminals, a sleeve of insulation surrounding saidterminals and said section, and a corona and radiation shieldinside saidsleeve and spaced therefrom and surrounding said section, said coronaand radiation shield being spaced from said fusible section with an airdielectric therebetween.

19. In a fuse link, a pair of fuse terminals, a fusible sectionconnecting said terminals, a sleeve of insulation surrounding saidterminals and said section, a corona and radiation shield inside saidsleeve and surrounding said section, and a spring connected between saidterminals to put said section under predetermined tension, the reactionof said springbeing taken up through said sleeve in compression.

20. In combination with a fuse link comprising a first fuse terminalmember, a second fuse terminal member, and a fusible element connectingsaid terminal members, a fiber tube having one end bound uponsaid firstmember, said member having a threaded stud projecting out of the end ofthe tube, aflexible lead connected to the second member, a springconnected between the second member and the tube'to tension the element,and a fitting having a flanged head at one end, a flat intermediateportion, and a tubular threaded socket at. the other end threaded uponsaid stud and constituting a terminal connector therefor.

21. In a fuse device, in combination, a fuse tube, a pair of terminalmembers inside said fuse tube, a strain element and a fusible elementdisposed to interconnect said terminal members, and a metal shieldinside said fuse tube and connected to one of said terminal members andextending along and out of contact engagement with said strain andfusible elements.

22. In a fuse device, in combination, a fuse tube, a pair of terminal.members, a strain element and a'fusible element composed of silver anddisposed to interconnect said terminal members, and a metal shieldconnected to one of said terminal members and extending along andslightly out of contact engagement with said strain and silver fusibleelements with an air dielectric therebetween to protect said fuse tubefrom the heat radiated b said silver fusible ele ment.

23. In a fuse device, incombination, a-fuse tube, a pair of terminalmembers inside said fuse tube, a strain element and a fusible elementdisposed to interconnect said terminal members. and a tubular metallicradiation shield connected to one of said terminal members andsurrounding said strain and fusible elements and slightly spacedtherefrom with an air dielectric therebetween.

24. In a fuse device, in combination, a pair of terminal members, astrain Wire interconnecting said terminal members, a fuse wire Wrappedaround said strain wire in close contact engagement therewith and alsointerconnecting said terminal members, and a metal shield connected toone of said terminal members and extending along and out of contactengagement with said strain and fuse wires, I g

25. In a fuse device, in combination, a pair of terminal members,astrain Wire interconnecting said terminal members, a fuse wire wrappedaround said strain wire in close contact engagement therewith and alsointerconnecting said terminal members, and a tubular metallic radiationand corona shield forming an extension of one of said terminal membersand extending toward the other terminal member out of contact engagementwith said strain and fuse wires.

26. In a fuse device, a stationary terminal, a fuse terminal attachedthereto, said fuse terminal comprising a tubular metallic shieldanchored to the stationary terminal, a fusible conductor also anchoredto the stationary terminal and extending through the tubular member, amovable fuse terminal secured to the fusible conductor and being spacedfrom the tubular member to provide a spark gap for protecting thefusible member from surges.

27. In a liquid fuse, the combination of a fuse tube having a ferrule, aterminal anchorage carried by said ferrule, a first fuse terminalconnected to the anchorage, a second fuse terminal, a fusible elementbetween said first and second terminals, a liquid director connected tothe second terminal, and a tubular shell mounted on said liquid directorand defining an arcing chamber loosely surrounding the fusible member.

28. In a liquid fuse, the combination of a fuse tube having a ferrule, aterminal anchorage carried by said ferrule, a firstfuse terminalconnected to the anchorage, a second fuse terminal, a fusible elementbetween said first and second terminals, and a tubular radiation shieldintegrally formed with one of said terminals and surrounding saidfusible member, said shield approaching the other terminal to provide asafety gap between said terminals and in parallel With said fusiblemember.

29. In a liquid fuse, the combination of a fuse tube having a ferrule, aterminal anchorage carried by saidferrule, a first fuse terminalconnected to the anchorage, a second fuse terminal, a fusible elementbetween said first and second terminals, a tubular shell defining anarcing chamber loosely surrounding said fusible element, and a tubularradiation shield integrally formed with one of said terminals andsurrounding said fusible member inside of said tubular shell, saidshield approaching the other terminal toprovide a safety gap betweensaid terminals and in parallel with said. fusible member.

30. In a fuse, a fusible element, fuse terminals connected to the endsof the fusible element, and conducting means connected to the fuseterminals and approaching each other to form a spark gap in parallelwith the fusibleelement.

31. In a fuse device, in combination, a pair of terminal members, a fuselink interconnecting said terminal members, a flexible conductorattached to one of said terminal members, and means for permitting lostmotion between a part of said conductor and the terminal member attachedthereto.

In. a fuse device, in combination, a pair of terminal members, a fuselink interconnecting said terminal members, means for mounting said fuselink in a fuse mounting including a flexible conductor disposed to bemanually tensioned,

and means for permitting a slight relative movement between a portion ofsaid conductor and the terminal member to which it is attached.

In a fuse device, in combination, a fuse link-having a substantiallyconstant time-cur;- rent fusing rating over a relatively great tensionrange on application thereto of a predetermined minimum tension, meansfor prestressing said link to said minimum tension, and means forlimiting the maximum tension applied to said link.

34. In a fuse device, in combination a fuse wire having a minimumultimate strength in tension of approximately twenty pounds and asubstantially constant time-current fusingrating at any tension up tothe application of said twenty pounds from a minimum tension ofapproximately fourpounds, and means for constantly applying said tensionof four pounds to said fuse wire.

35. .In a fuse device, in combination, a metallic tubular fitting havingone end pinched on a fuse wire and the other pinched on a flexibleconductor, said pinched portions being disposed substantially at rightangles to each other, and a tension spring having its end convolutionclosely engaging the base of the portion of said fitting pinched on saidfuse wire and the next convolution surrounding the portion of saidfitting pinched on said flexible conductor.

36. In a fuse device, in combination, a pair of terminals, a fusibleelement interconnecting said terminals, a flexible lead attached to oneof said terminals, a retaining member secured to said flexible lead, anda helical spring interconnecting said terminal member to which said leadis attached and said retaining member, a convolution at one end of saidspring being reduced to a diameter about the periphery of one of saidlast named members less than the outside diameter of the spring fornon-rotative engagement therewith.

37. In a liquid fuse, the combination of a fuse tube having a ferrule, aterminal anchorage carried by said ferrule, a first fuse terminalconnected to the anchorage, a second fuse terminal, a fusible elementbetween said first and second terminals. a liquid director connected tothe second terminal, and a tubular shell defining an arcing chamberloosely surrounding the fusible member, one of said terminal membershaving an integral tubular radiation shield surrounding the fusiblemember and approaching the other terminal member to provide a safety gapbetween the terminal members and in parallel with the fusible member.

38. In a fuse device, in combination, a fuse tube formed of a materialliable to be injured when subjected to high temperature, a pair ofterminals inside said fuse tube, a silver fusible sectioninterconnecting said terminals, and a metal shield spaced from saidsilver fusible section to protect the inner surface of said fuse tubefrom the heat radiated by said silver fusible section.

39. In a fuse device, in combination, a fuse tube formed of a materialliable to be injured when subjected to high temperature, a pair ofterminals inside said fuse tube, a silver fusible sectioninterconnecting said terminals, and a metal shield connected to one ofsaid terminals and extending along and spaced from said silver fusiblesection to protect the inner surface of said fuse tube from the heatradiated by said silver fusible section under normal operatingconditions.

40. A fuse link for completing a circuit between a pair of stationaryline terminals comprising, in combination, a pair of fuse terminals oneof which is adapted to be connected to one of said line terminals, afusible section interconnecting said fuse terminals, an insulating tubesupporting said one fuse terminal and surrounding said fusible section,a flexible lead interconnecting the other fuse terminal and the otherline terminal, and a spring interposed between said tube and said otherfuse terminal tc place said fusible section under stress independent ofthe connections to said line terminals.

41. 'In a fuse device, a stationary terminal, a fuse terminal attachedthereto, a fusible conductor anchored to said fuse terminal, a movablefuse terminal secured to said fusible conductor, and a metallic shieldcarried by one of said fuse terminals and extending toward the otherfuse terminal to provide a spark gap for protecting said fusibleconductor from surges.

42. In a liquid fuse, in combination, a fuse tube having a ferrule, afirst fuse terminal connected to said ferrule, a second fuse terminal, afusible element between said first and second terminals, and a tubularshell carried by said second fuse terminal and loosely surrounding saidfusible element and defining an arcing chamber.

43. In a liquid fuse, a fusible element, fuse terminals connected to theends of the fusible element, and conducting means carried by one of saidfuse terminals and extending toward the other fuse terminal to provide aspark gap above the level of the liquid in the fuse for protecting saidfusible element from surges.

44. A replaceable fuse link adapted for mounting in an insulating fusehousing of the expulsion type comprising, a pair of terminals, a fusiblesection interconnecting said terminals, spring means biasing saidterminals apart, and a tubular metal corona shield extending from one ofsaid terminals and surrounding said fusible section and being unstressedby said spring means.

45. A replaceable fuse link adapted for mounting with its fusiblesection entirely within an insulating fuse tube of the expulsion typecomprising, a pair of terminals, a fusible section interconnecting saidterminals, an insulating sleeve surrounding said fusible section andadapted to evolve an arc extinguishing medium under the action of theare formed on blowing of said fusible section, and a tubular metalcorona shield extending from one of said terminals and surrounding saidfusible section.

46. A replaceable fuse link adapted for mounting with its fusiblesection entirely Within an insulating fuse tube of the expulsion typecomprising, a pair of terminals, a fusible section interconnecting saidterminals, an insulating sleeve surrounding said fusible section, springmeans biasing said terminals apart, and a tubular metal corona shieldextending from one of said terminals toward the other terminal andsurrounding said fusible section and being unstressed by said springmeans.

47. A replaceable fuse link comprising, a pair of relatively infusibleterminals, a fusible section interconnecting said terminals, and aninherently rigid metal shield extending from one of said terminalstoward the other and surrounding said fusible section.

48. A replaceable fuse link comprising, a pair of relatively infusibleterminals, a fusible section interconnecting said terminals, and aninherently rigid tubular metal shield surrounding said fusible sectionand extending from one of said terminals toward the other to formtherewith a spark gap in parallel with said fusible section.

49. A replaceablefuse link comprising, an insulating sleeve, arelatively infusible terminal at one end of said sleeve, a conductorincluding a relatively infusible terminal and aflexible lead extendingoutof the other end of said sleeve, a fusible section electricallyinterconnecting said terminals, and an inherently rigid tubular metalshield surrounding said fusible section and extending from one of saidterminals toward the other to form therewith a spark gap in parallelwith said fusible section.

, 50. In a liquid fuse, a terminal for a fusible section positionedabove the level of the liquid when the fuse is in an uprightposition,and a tubular metal corona shield for surrounding the fusiblesection, said shield extending downwardly from said terminal and havingan aperture in its wall to prevent retention of the liquid within theshield when the fuse is in the upright position,

whereby the predetermined time-current characteristic of the fusiblesection is not affected.

51. In a replaceable fuse link, in combination, a terminal member, ananchor member, a spring non-rotatively secured at its ends to saidterminal and anchor members respectively, said members being spacedapart a predetermined distance whereby said spring is normally stressed,and a flexible lead mechanically interconnecting said members and ofsuch length therebetween that it is substantially unstressed when theyare spaced apart at said predetermined distance.

52. In a fuse, a fitting comprising a terminal and radiation shieldmember consisting of a first tubular portion adapted to embrace looselya fusible section and a second tubular portion of smaller diameter thanthe first tubular portion adapted to be pinched upon one end ofthefusible section.

53. A terminal for a renewable fuse link for rendering the same capableof being connected into fuse mountings of different types comprising, ahead, and a flat shank, said flat shank being partially severed at thebase of said head in the direction of its depth thus permittingsubsequent detachment of said head to facilitate clamping to said shank,the shank being partially severed in permitting subsequent detachment ofa portion of the shank to facilitate clamping, the shank being partiallysevered in such manner that the electrical conductivity of the terminalis only slightly reduced.

55. A terminal for a renewable fuse link for .rendering the same capableof being connected into fuse mountings of different types comprising, ahead, and a flat shank, said flat shank being provided with a generallyU-shaped portion partially severed in the direction of its depth thuspermitting subsequent detachment of this 'U- shaped portion tofacilitate clamping, the shank being partially severed in such mannerthat the electrical conductivity of the terminal is only slightlyreduced.

56. A renewable fuse link comprising, a fuse tube, a terminal at one endof said fuse tube, a 'conductor including a flexible lead extending outof the other end of said fuse tube, and fusible means interconnectingone end of said terminal and said conductor, said terminal having aflanged head at its other end and a flat portion intermediate its ends,sald'flat portion having a generally U-shaped section opening along oneside and partially severed in the direction of its depth thus permittingsubsequent detachment of this section to facilitate clamping, thesection being partially severed from'said flat portion in from said flatintermediate portion in the direction of its depth whereby it serves asan electrical connecting portion and may be removed to provide forclamping said intermediate portion to a flat contact surface.

58. In a renewable fuse link adapted for use in a drop-out fuse tubewhich is normally held in operative position by tension transmittedthrough the fuse link, in combination, means for imposing a minimumtension on the fusible sec tion of the link whether or not it is mountedin the fuse tube, and means preventing said minimum tension beingcumulative with the tension holding the fuse tube in operative position.

59. In a renewable fuse link adapted for use in a fuse tube undertension, means including a spring and a strut member cooperating toimpose a minimum tension on the fusible section ,of the link beforeinsertion in the fuse tube and arin the fuse tube from furthertensioning the fusi-' ble section until the externally applied tensionexceeds said minimum tension.

60. In a dropout fuse device, in combination, a fuse housing arrangedand adapted to be slammed to the circuit closed position; a renewablefuse link in said fuse housing including a fuse tube, a terminal at oneend of said fuse tube, a flexible lead extending out of the other end ofsaid fuse tube, fusible means interconnecting said terminal and saidflexible lead, and sprin means tensioning said fusible means in suchmanner that tension stress externally applied to said flexible lead isnot cumulative with the tension applied by said spring means; saidterminal and flexible lead being connected to said fuse housing in suchmanner as to hold the same latched in the circuit closed position, and asecond spring cooperating with said fuse housing and restrained by saidfuse link for unlatching the former on blowing of the latter. I

61. In a dropout fuse device, in combination, a

I fuse housing arranged and adapted to be slammed -portion of'saidflexible leadextending out ofsaid sleeve; said one terminaland saidflexible lead

